Patent Document 1 discloses a battery temperature-control device as a prior art example of a battery pack.
The battery temperature-control device of Patent Document 1 includes a main battery including a unit of cells, a sheet heater that is heated when supplied with current, and a temperature sensor that detects the temperature of the battery. The sheet heater, which is located between the cells, is arranged at two locations in contact with all of the cells. A heater that generates heat when supplied with current is incorporated in the sheet heater.
When the temperature detected by the temperature sensor is lower than a certain value, an auxiliary battery applies current to the sheet heater to control the temperature of the main battery with the heat of the sheet heater. This maintains the main battery at a proper temperature and prevents reduction in the battery capacity even during the winter.